WAVE OF SUPPORT: President Obama salutes the massive crowd that gathered yesterday in Washington to hear him deliver his second Inaugural Address. Photo: Reuters

SHOWING THE LOVE: President Obama blows a kiss to throngs of supporters as he and First Lady Michelle parade along Pennsylvania Avenue in Washington yesterday. (AP)

STANDING ROOM ONLY: Hundreds of thousands of spectators fill the National Mall. (EPA)

RED, WHITE & WOOHOO: Revelers celebrate at the Mall. (EPA)

WAVE OF SUPPORT: President Obama salutes the massive crowd that gathered yesterday in Washington to hear him deliver his second Inaugural Address. (Reuters)

WASHINGTON — President Obama yesterday delivered a full-throated call for a bold liberal agenda, vowing in his Inaugural Address to take aggressive action on climate change, gay rights and immigration reform during his second term.

“America’s possibilities are limitless,” Obama declared as he teed up a to-do list destined to encounter fierce opposition from Republicans. “My fellow Americans, we are made for this moment, and we will seize it, so long as we seize it together.”

The 19-minute speech, delivered from a stage outside the Capitol, set a series of ambitious markers for Obama’s next four years in office.

Seizing upon the coincidence that his inauguration fell on Martin Luther King Jr. Day, America’s first black president recalled the country’s civil-rights struggle to argue that his agenda has a moral imperative.

“Now, more than ever, we must do these things together, as one nation and one people,” he said.

About 800,000 people crowded the National Mall to cheer Obama, less than half the record 1.8 million who showed up for his historic inauguration four years ago.

Obama, who no longer has to face voters at the ballot box, went out of his way to confront Tea Party members and other conservative Republicans who have been the staunchest critics of unchecked spending and of the more than $16.4 trillion in federal debt.

The president defended America’s growing entitlement programs.

“The commitments we make to each other through Medicare and Medicaid and Social Security, these things do not sap our initiative, they strengthen us,” he said, directly challenging GOP calls for reform.

“They do not make us a nation of takers; they free us to take the risks that make this country great,” he said in what sounded like a swipe at comments by Republican vice-presidential candidate Paul Ryan during the 2012 campaign.

“We must make the hard choices to reduce the cost of health care and the size of our deficit,” he said. “But we reject the belief that America must choose between caring for the generation that built this country and investing in the generation that will build its future.”

Obama vowed to tackle climate change, an issue he rarely mentioned during his re-election campaign amid a shaky economy.

“We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations,” he said. “Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires and crippling drought and more powerful storms.”

Using cadences reminiscent of Dr. King’s iconic speeches, Obama invoked Seneca Falls, the march at Selma, Ala., and the Stonewall riots — three key moments in the struggles for women’s rights, civil rights and gay rights, respectively.

“Our journey is not complete until our wives, our mothers and daughters can earn a living equal to their efforts. Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law, for if we are truly created equal, then surely, the love we commit to one another must be equal as well. Our journey is not complete until no citizen is forced to wait for hours to exercise the right to vote,” he said.

And he promised to confront immigration reform and overhaul gun laws in the wake of the Sandy Hook massacre.

“Our journey is not complete until we find a better way to welcome the striving, hopeful immigrants who still see America as a land of opportunity, until bright young students and engineers are enlisted in our workforce rather than expelled from our country,” Obama said.

“Our journey is not complete until all our children — from the streets of Detroit to the hills of Appalachia to the quiet lanes of Newtown — know that they are cared for and cherished and always safe from harm.”

And he took aim at his budget foes.

“For now, decisions are upon us and we cannot afford delay. We cannot mistake absolutism for principle or substitute spectacle for politics or treat name-calling as reasoned debate,” he said.

Republican lawmakers said they were surprised by the partisan, leftward tilt.

“It was definitely liberal in tone, much more than I would expect in an inaugural speech,” said Rep. Peter King (R-LI). “What bothers me is that I thought parts of it [were] more of a campaign speech than an inaugural address. He’s implying that he wants to take care of disabled kids and Republicans don’t. I think we could have done without the partisan shots. All of that to me was inappropriate.”

“The president unequivocally affirms that he believes that government is good and needs to be stronger,” Sessions said. “I’m very worried if the president of the United States does not understand that in our great expansion of our social and welfare programs, there is a danger of dependency being created.”

But Sen. John McCain (R-Ariz.), who lost to Obama in the 2008 presidential election, didn’t begrudge him the chance to kick off his term with bold challenges. Still, he expected him to be more conciliatory.

“The president won the election. He has favorable ratings with the American people. Everything I’ve been told is that he’s going to pursue that agenda in his second term. He campaigned on that, so it’s not as if it comes as a surprise,” said McCain.

But, he added, “I would have loved to have seen some more about national security, and I would have liked to have seen at least a sentence about us having to work together.”

Obama delivered his call for social justice on a day filled with pomp, pageantry, and celebrity glitz.

Katy Perry, John Mayer, and Eva Longoria were among the celebrities with good seats.

Sen. Charles Schumer (D-N.Y.) delivered a long invocation, then played the role of emcee introducing each speaker and performer, stressing his hometown when introducing the Brooklyn Tabernacle Choir.

“Wow!” he said after Kelly Clarkson ripped through “My Country ‘Tis of Thee,” backed by the U.S. Marine Band.